SVNWebClient would always use the Subversion user accounts as it needs to perform reading and writing of repository resources on behalf of a concrete user.

So you can either configure your Subversion repository to use an authentication mean applicable for you (like connecting to a DB instead of plain passwd file), SVNWebClient would use that authentication transparently, or you can try to reimplement the authentication layer of SVNWebClient to suit your needs.

So you can either configure your Subversion repository to use an authentication mean applicable for you (like connecting to a DB instead of plain passwd file), SVNWebClient would use that authentication transparently, or you can try to reimplement the authentication layer of SVNWebClient to suit your needs.